The Detective Aboard NASA's Perseverance Rover
An instrument called SHERLOC will, with the help of its partner WATSON, hunt for signs of ancient life by detecting organic molecules and minerals.
Mars is a long way from 221B Baker Street, but one of
fiction's best-known detectives will be represented on the Red Planet after
NASA's Perseverance rover touches down on Feb. 18, 2021. SHERLOC, an instrument
on the end of the rover's robotic arm, will hunt for sand-grain-sized clues in
Martian rocks while working in tandem with WATSON, a camera that will take
close-up pictures of rock textures. Together, they will study rock surfaces,
mapping out the presence of certain minerals and organic molecules, which are
the carbon-based building blocks of life on Earth.
SHERLOC was built at NASA's Jet Propulsion Laboratory in
Southern California, which leads the Perseverance mission; WATSON was built at
Malin Space Science Systems in San Diego. For the most promising rocks, the Perseverance
team will command the rover to take half-inch-wide core samples, store and seal
them in metal tubes, and deposit them on the surface of Mars so that a future
mission can return them to Earth for more detailed study.
SHERLOC will be working with six other instruments aboard
Perseverance to give us a clearer understanding of Mars. It's even helping the
effort to create spacesuits that will hold up in the Martian environment when
humans set foot on the Red Planet. Here's a closer look.
The Power of Raman
SHERLOC's full name is a mouthful: Scanning Habitable Environments with Raman &
Luminescence for Organics & Chemicals. "Raman" refers to Raman
spectroscopy, a scientific technique named after the Indian physicist C.V.
Raman, who discovered the light-scattering effect in the 1920s.
"While traveling by ship, he was trying to discover why
the color of the sea was blue," said Luther Beegle of JPL, SHERLOC's
principal investigator. "He realized if you shine a light beam on a
surface, it can change the wavelength of scattered light depending on the
materials in that surface. "
This effect is called Raman scattering. Scientists can
identify different molecules based on the distinctive spectral
"fingerprint" visible in their emitted light. An ultraviolet laser
that is part of SHERLOC will allow the team to classify organics and minerals
present in a rock and understand the environment in which the rock formed. Salty
water, for example, can result in the formation of different minerals than
fresh water. The team will also be looking for astrobiology clues in the form
of organic molecules, which among other things, serve as potential
biosignatures, demonstrating the presence life in Mars' ancient past.
"Life is clumpy," Beegle said. "If we see
organics clumping together on one part of a rock, it might be a sign that
microbes thrived there in the past."
Nonbiological processes can also form organics, so detecting
the compounds isn't a sure sign that life formed on Mars. But organics are crucial
to understanding whether the ancient environment could have supported life.
A Martian Magnifying
Glass
When Beegle and his team spot an interesting rock, they'll
scan a quarter-sized area of it with SHERLOC's laser to tease out the mineral
composition and whether organic compounds are present. Then WATSON (Wide Angle Topographic Sensor for
Operations and eNgineering) will take close-up images of the sample. It can snap images of Perseverance,
too, just as NASA's Curiosity rover uses the same camera - called the Mars Hand
Lens Imager on that vehicle - for science and for taking selfies.
But combined with SHERLOC, WATSON can do even more: The
team can precisely map SHERLOC's findings over WATSON's images to help reveal
how different mineral layers formed and overlap. They can also combine the
mineral maps with data from other instruments - among them, PIXL (Planetary Instrument for X-ray
Lithochemistry) on Perseverance's robotic arm - to see whether a rock could
hold signs of fossilized microbial life.
Meteorites and Spacesuits
Any science instrument
exposed to the Martian environment for long enough is bound to change, either
from the extreme temperature swings or the radiation from the Sun and cosmic
rays. Scientists occasionally have to calibrate these instruments, which they
do by measuring their readings against calibration targets - essentially,
objects with known properties selected in advance for cross-checking purposes. (For
instance, a penny serves as one calibration target aboard Curiosity.) Since they
know in advance what the readings should be when an instrument is working
correctly, scientists can make adjustments accordingly.
About the size
of a smartphone, SHERLOC's calibration target includes 10 objects, including a
sample of a Martian meteorite that traveled to Earth and was found in
the Oman desert in 1999. Studying how this meteorite fragment changes over the
course of the mission will help scientists understand the chemical interactions
between the planet's surface and its atmosphere. SuperCam, another instrument aboard
Perseverance, has a piece of Martian meteorite on its calibration target as
well.
While scientists
are returning fragments of Mars back to the surface of the Red Planet to
further their studies, they're counting on Perserverance to gather dozens of
rock and soil samples for future return to Earth. The samples the rover collects
will be exhaustively studied, with data taken from the landscape in which they
formed, and they'll include different rock types than the meteorites.
Next to the
Martian meteorite are five samples of spacesuit fabric and helmet material developed by NASA's Johnson Space
Center. SHERLOC will take readings of these materials as they change in the
Martian landscape over time, giving spacesuit designers a better idea of how
they degrade. When the first astronauts step on to Mars, they might have
SHERLOC to thank for the suits that keep them safe.
About the Mission
Perseverance is a robotic
scientist weighing about 2,260 pounds (1,025 kilograms). The rover's astrobiology
mission will search for signs of past microbial life. It will characterize the
planet's climate and geology, collect samples for future return to Earth, and
pave the way for human exploration of the Red Planet. No matter what day
Perseverance launches during its July 17-Aug. 11 launch period, it will land at
Mars' Jezero Crater on Feb. 18, 2021.
The Mars 2020 Perseverance
rover mission is part of a larger program that includes missions to the Moon as
a way to prepare for human exploration of the Red Planet. Charged with
returning astronauts to the Moon by 2024, NASA will establish a sustained human
presence on and around the Moon by 2028 through the agency's Artemis lunar exploration plans.
For more
about Perseverance:
https://mars.nasa.gov/mars2020/
https://nasa.gov/perseverance
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